Several in vivo and in vitro development changes have been characterized in collagen- and mucopolysaccharide-producing cells from chick embryos and these systems will serve as the foci for continuing work. Factors affecting rates of synthesis of chondroitin sulfate and collagen will be studied in detail. The effects of chick embryo extract on increasing ratios of chondroitin sulfate to hyaluronic acid synthesized by chondrocytes as they grow to confluence in culture will be examined. The rates of biosynthesis of collagen, chondroitin sulfate, and hyaluronic acid by cultured chondrocytes taken from different regions of the embryonic tibia of different aged embryos will be measured. (There are four distinct regions of the tibia in which the chondrocytes show distinctive cell morphologies even though all of these cells are derived from cells in the epiphyseal plate.) Finally it is planned to study the biosynthesis of dermatan sulfate in fibroblasts prepared from chick embryo aortas with special emphasis on the relative rates of loss of capacities to synthesize dermatan sulfate and chondroitin sulfate as these cells dedifferentiate in culture. In each of the above systems, attempts will be made to demonstrate changes in cell surface carbohydrates as cells undergo changes in their differentiated state.